Existing grain dryers typically utilize a plurality of polygonal-shaped grain conduits with a longitudinal central opening defining a heat plenum through which hot air is driven by a fan. At least the inner walls of the conduits that define the heat plenum are perforated to permit the air to pass therethrough to dry the grain within the conduits. The grain is introduced at the top of the dryer into the conduits and moves by gravity downwardly through the conduits for discharge at the bottom of the dryer.
It is known to stack such dryer units one on top of another in a double or triple stack. In such stack dryers, the conduits extend down opposite sides of the dryers from the top of the upper-most dryer unit to the bottom of the lowered dryer unit. In such stack dryers, the grain adjacent the inside wall of the conduit in closest proximity to the heat plenums becomes over dried and damaged, while grain adjacent the outer walls of the conduits furthest from the heat plenums may not be sufficiently dried. Thus, a non-uniform quality of grain dryness results.
Also, environmental factors such as wind can have a drastic effect on the moisture content of the grain in a stack grain dryer. Winds of 10-20 miles per hour can substantially reduce the drying efficiency of the dryer, such that grain on the exposed side is not as dry as grain on the opposite side, which is protected from the wind.
Prior art dryers have also attempted to increase uniformity of drying by providing internal deflectors or vanes which direct the grain between opposite walls. The Kyle U.S. Pat. No. 3,751,824 discloses such a dryer having internal deflector chutes for inverting the grain flow within each side of the dryer. However, such internal walls or deflectors are subject to plugging due to material or debris catching on the internal conduit structure.
Therefore, a primary objective of the present invention is the provision of an improved stack dryer for drying grain.
Another objective of the present invention is the provision of a stack grain dryer having crossover grain conduits so as to provide improved uniformity of drying of the grain.
Another objective of the present invention is the provision of an improved stack dryer for grain wherein the grain conduits crossover between the upper and lower dryer units so as to expose different portions of the grain to the highest heat intensity from the heat plenums.
A further objective of the present invention is the provision of an improved stack dryer for grain wherein the grain is moved from one side of the dryer to the opposite side of the dryer so as to minimize adverse effects of wind on grain drying.
Another objective of the present invention is the provision of an improved method of drying grain in a stack grain dryer.
These and other objectives will become apparent from the following description of the invention.
A stack grain dryer is provided with upper and lower dryer units with grain conduits extending along each side of the central heat plenums. Each conduit has an upper section and a lower section, with an intermediate crossover section, such that the upper sections of the conduits extend along one side of the upper heat plenum and the lower sections of the conduits extend along the opposite side of the lower heat plenum. Thus, the grain flowing along the inner wall of the upper conduit section flows along the outer wall of the lower conduit section. Similarly, the grain flowing along the outer wall of the upper conduit sections flows along the inner wall of the lower conduit section. By moving the grain from one side of the dryer to the opposite side of the dryer during the drying process, via the crossover conduits, the grain is protected from the wind for approximately one-half of the drying process, thereby balancing moisture content of the grain on both sides of the dryer. Accordingly, improved uniformity of grain dryness is achieved with the crossover conduits of the stack dryer.